The generation of electricity from wind power is well known in the art. However, although wind power is known to be one of the most valuable sources of renewable energy, it has been characterised by moderate to very large wind turbines, typically grouped together in “wind farms”. Well known are large scale Horizontal Axis Wind Turbines, or HAWTs, which are the familiar tower mounted propellers, with a rear mounted alternator, and which can be as high as several hundred feet tall and hundreds of feet in diameter. Other less common designs of large-scale wind turbine comprise Savonius rotors or Darrieus rotors, as described in U.S. Pat. No. 1,697,574 and U.S. Pat. No. 1,835,018 respectively.
HAWTs disadvantageously lead to visual intrusion, safety concerns, destruction of bird and bat life as well as serious disruption to airborne and ground based radar systems, due to both the large rotating surfaces and atmospheric disturbances behind the turbines. Further considerations are the impact of noise emanating from the wingtips, which rotate at high speeds, and the large amounts of energy used to produce the high grade materials used in their construction. Also, such HAWTs are exposed to the elements in all conditions, and accordingly are vulnerable to damage during extreme weather conditions. Yet further, such HAWTs are typically grouped into “wind farms” in rural locations, remote from energy consumers leading to associated cost and inefficiencies in the distribution of the generated electricity.
Accordingly, interest has grown in the provision of wind-turbines that may be located on buildings and having cross-flow, horizontal axis, elongate rotors of generally cylindrical shape, typically of the paddle wheel, Savonius or Darrieus types.
Although it is known to mount the rotor directly to the ridge (apex) of a roof, as disclosed in US20090304512 and DE202008014689, it is preferable to locate the rotor within a housing for aesthetic and structural reasons.
JP200365206 discloses a wind turbine comprising a housing mounted onto the ridge of a roof and having a plurality of rotors mounted parallel with the roof ridge. Disadvantageously, the housing of JP200365206 provides only a limited protection to the rotors in the case of high wind, such that the wind turbine is vulnerable to damage in high winds. Also in high winds the rotation of the rotor may be too high for the operational capacity of the power generation system.
WO2009009701 discloses a wind turbine having a cylindrical housing that is mounted onto the apex of a roof. The housing has pivotable air flow guides that may be dynamically angled. To provide protection to the rotor, the air flow guides may be closed in high wind conditions. Disadvantageously, the air flow guides are directly exposed to high winds and are susceptible to damage.
JP2003129941 discloses a wind turbine within a funnel shaped housing for mounting on the ridge of a roof. The rotor is provided with a wind flow control element, that comprises a cylindrical member surrounding the rotor and having an inlet and outlet slit, which may be orientated in one of two configurations, subject to the prevailing wind direction. Damage to the rotor in high winds is prevented by lowering air deflector flaps to close the housing. Disadvantageously, such a wind turbine is complex and expensive. Further, the closable flaps remain directly exposed to high winds, and so are susceptible to damage.
JP2006266236 discloses a wind turbine having a funnel-shaped housing mounted on the ridge of a roof, and within which cross-flow, horizontal axis, elongate rotor of generally cylindrical shape is mounted for rotation about an axis parallel with the roof ridge. A wind attenuator is provided within the housing, comprising a cylindrical screen having two quarters having wide openings, and the two remaining quarters having screens with slit-like openings. The wind attenuator is ordinarily held in an unattenuated orientation, in which the wide openings align with the inlet and outlet of the housing. The wind attenuator is biased to rotate about the axis of the rotor into an attenuated orientation. When the wind speed exceeds a predetermined speed, a wind sensing plate is blown over, disengaging a locking mechanism, such that the wind attenuator rotates into the attenuated orientation. In the attenuated orientation, wind passes through the slit-like openings, but at a rate that is reduced relative to that which passes through the wide openings in the unattentuated orientation. Disadvantageously, the device of JP2006266236 is only capable of operating with the wind attenuator in an unattenuated orientation or an attenuated orientation. Consequently, wind exposure of the rotor cannot be optimised to maximise energy generation. Further, the rotor cannot be completely shielded from the wind in high wind conditions or during maintenance. Such a mechanically operated mechanism is vulnerable to manufacturing tolerances, as well as mechanical wear over the operational lifetime. The method of resetting the wind attenuator into the unattenuated position is not disclosed.
The present invention seeks to address at least some of the problems mentioned above.